Polymer plastics because of there inherent characteristics are often preferred for use in medical applications such as tooth and bone implants. Unfortunately, one of the problems with plastics is that when the implanted plastic article is subjected to x-rays the resulting image of most plastics is not detectable on the x-ray picture. In order to solve this problem it is well known to mix metals or other materials into the plastics to produce a material that when x-rayed produces an x-ray picture that contrasts with the body. One of the difficulties with mixing polymer plastics with metals or other radio opaque compounds is that it weakens the plastic. In some cases this can be tolerated but in other cases substantial weaken of the plastic is not acceptable.
Another difficulty is to mix materials into the plastic to improve the radio opacity of the plastics without having the added materials effect the mixing process. For example, heating a composition of a plastic and a radio opaque additive to the melting temperature of the plastic so that one can mold the composition into a homogeneous product may result in oxidation of the added materials. Consequently, when mixing radio opaque materials into the polymer plastics one must prevent the molding process of the plastic and the radio opaque materials from interfering and destroying each other. The present invention solves the problem of mixing radio opaque materials into certain polymer plastics to produce a molded plastic product is radio opaque so that when the x-rayed the presence of the molded plastic product appears on an x-ray picture of the molded plastic product.
Another difficulty with use of plastic materials in place of metals is that even if materials have been added to the plastic to make the plastic radio opaque the radio opacity of the resulting material may not have the correct degree of radio opacity for the particular application. For example, in one application, which is described in U.S. Pat. No. 4,758,156, a cone of gutta-percha is placed outside of a tooth implant comprising an elongated shaft. The composite insert comprising the tooth implant and the gutta-percha is then inserted into a root canal of a tooth to form a filling for the tooth. If a metal is used as the tooth implant then the resulting x-ray image of the tooth with the filling comprising the combination of gutta-percha and the metal tool appears as a single image in an x-ray image of the tooth. Although two materials are present it is desired to have the x-ray image of the two materials appear as a single image in such applications. However, when one uses plastic in place of the metal in the tooth implant the resulting x-ray image appears as two distinct materials. One of the problems the present invention solves is to make two distinct materials appear as one image when subjected to x-rays. Not only is it necessary to make the two materials appear as one when x-rayed but it is also necessary to prevent the addition of radio opaque filler materials to the tooth implant from weakening the tooth implant. That is, if one mixes radio opaque materials into the filler material used to make the tooth implant the radio opaque material acts as a spacer and filler to the composition and may weaken the tool to the point where the tool is not sufficiently strong for use in the intended manner. When a tooth implant is used in the intended manner the user can insert both the tooth implant and a gutta-percha filler material into the bottom of the root canal without breaking the tool. Thus a person is faced with the simultaneous tasks of making a sufficiently strong tooth implant and also having two different filler materials that when x-rayed produce a single x-ray image without any interface areas between the two materials showing up as a void or cavity in the tooth.
The present invention involves a discovery that the combination of selected amounts of heavy metals with a thermoplastic polymer provides a radio opaque article. In addition it has been found that combination of selected amounts of heavy metals with a thermoplastic polymer filler material mixture also can be used to mold a body implant that is detectable by x-rays. It also has been discovered that the use of my composition in tooth implants for insertion into a root canal as a permanent implant is sufficiently strong to us to force gutta-percha filler material or gutta-percha like material and the tooth implant into a root canal. In addition, x-ray post examination of a tooth filled with a severed portion of a dental tool made from the composition of the present invention and a different filler material reveals a single image. That is, it has been discovered that when a tooth is x-rayed that contains an insert made from my invention that contains a combination of selected amounts of a heavy metals with a thermoplastic polymer that is surrounded by a layer of gutta-percha one obtains a single photoshadowgraph image. This single image occurs even tho two distinct material having distinct interfaces are located in the root canal. Consequently, even tho two different filler materials are located in a coaxially, separate relationship in a tooth, the x-ray image of the severed end of the tooth implant surrounded by a cone of gutta-percha appears as a single uniform image on an x-ray picture of a filled tooth. Ironically, the use of two different materials to create a false image of what is actually present in the tooth is preferred since it ensures that during a later x-ray examination of a filled tooth the practitioner will not be falsely deceived into believing that the tooth has a void or cavity.
Further background on the concept of applying filler material to an endodontically prepared root canal is described in U.S. Pat. No. 4,758,156. Briefly, the patent discloses a tooth implant having an elongated severable shaft coated with a cone of gutta-percha. To insert the tooth implant and the gutta-percha into a root canal the gutta-percha is heated to make it flowable. Then the elongated severable stiff but resilient end of the tooth implant with the flowable gutta-percha is used to push both the gutta-percha and the end of the tooth implant into the root canal. Once the gutta-percha and the elongated severable end of the tool compactly fill any voids in the root canal the user twists the handle of the tooth implant to break off the severable end of the tool thereby leaving both the severed end of the tooth implant and the gutta-percha as filler material in the root canal. Typically, the tooth implant is made of either a metal or a plastic so as to have sufficient strength and flexibility to permit a dentist to push both the elongated shaft of the tooth implant and the gutta-percha into the bottom of the root canal. Unfortunately, unless the shaft is metal a photoshadowgraph (commonly referred to as x-rays) or x-ray image of a tooth with two different filler materials appears on an x-ray picture as two distinct images with a void between the two filler materials. The appearances of two distinct x-ray images may lead false post x-ray examinations where the dentist is led to believe that the x-rayed tooth was not properly filled or that the tooth contains a cavity.
In order to eliminate false diagnose caused by the x-ray images produced by the two dissimilar materials one needs to eliminate the x-ray appearance of the two dissimilar materials that leads an observer to believe the tooth contains a cavity. The present invention solves the problem of making a plastic implant appear as the surrounding gutta-percha filler on an x-ray image of the plastic implant and the surrounding gutta-percha.